Low noise linear power supply schematics

Thread Starter

bjornkarl

Joined Mar 14, 2021
8
I'm looking for a help in suggesting an appropriate circuit diagram for a very low noise linear power supply with output of 5.1VDC nominal. The load is varying between min 60 and max 120mA. I already have a 120VAC/10VA R-Core transformer with 12VAC output available and was thinking it could perhaps be used for this?
 

dl324

Joined Mar 30, 2015
12,678
Welcome to AAC!

With a 12VAC secondary and a 5.1V output voltage, you should have no problems with noise from a commercial linear voltage regulator. Unless your definition of very low noise is unreasonable.
 

Thread Starter

bjornkarl

Joined Mar 14, 2021
8
Thanks Dennis! I have not been able to find a low power regulator such as this so I wanted to try and build one. But I'm not really good at circuit design :(
 

dl324

Joined Mar 30, 2015
12,678
I have not been able to find a low power regulator such as this so I wanted to try and build one. But I'm not really good at circuit design
From National Semiconductor:
clipimage.jpg
Worst case load regulation is 1% for LM317A.

Since the regulator has a lot of headroom, you don't need much filter cap after the rectifier.
 

Thread Starter

bjornkarl

Joined Mar 14, 2021
8
So how low is "low"?
That will allow better recommendations from us.
I can buy a very low regulated power supply for this audio application but it is only available as a dual output version with 2x5VDC outputs, one of which is 3.5A and the other 1.5A (cost is $165)- in other words "an overkill for my application. That power supply has a verified noise level of less than 0.08uV in the audio frequency range and it is considered "superior" for audio applications. I think their design includes "supercapacitors". What I'm looking for is a much lower power, single supply output and if there is a way to get the noise down to a similar level or thereabout I would be very happy.
 

Thread Starter

bjornkarl

Joined Mar 14, 2021
8
Not really sure that I really need that exact low level. But the power supply that I mentioned has been measured at that level. I will use the intended power supply to power the so called "clean side of an Allo DigiOne Signature HAT for Raspberry Pi4B having an SPDIF Coax output All reviewers of this device performance complain about audible noise if the HAT is powered by a regular switched power supply. Thus many users buy the commercially availably Linear Power supply mentioned previously (at $165). My thinking is that I will use a regular switched power supply to power the RPi while using the requested design for the clean side of the DigiOne board (the "clean" side of the board is galvanically isolated from from the RPi power supply so that any noise from the Rpi and the rest of the HAT is avoided).
 

crutschow

Joined Mar 14, 2008
26,737
Well, I doubt you need that low a noise for your application, and standard low-noise IC regulator should suffice.
If you Google low-noise IC regulators you will get many hits (here's an example).
I would think that a power supply noise of a few tens of microvolts should be more than sufficient for you application.
 

dl324

Joined Mar 30, 2015
12,678
Thus many users buy the commercially availably Linear Power supply mentioned previously (at $165).
Audiophiles make a number of outrageous claims. They say they can hear the difference between low oxygen copper and regular cables. Some even claim they can hear artifacts from wire splices.

Some people use carbon composition resistors because they say they like the distortion they introduce. Unfortunately, you need to be operating at over 100V to get that effect (as I recall).
 

Thread Starter

bjornkarl

Joined Mar 14, 2021
8
Dennis,
I'm fully aware that some Audiophiles makes such claims. But not all of them. There is some people (like me) that would listen to music from a simple cheap device rather than not listening to music at all. But, in the case I have discussed here I have had the privilege of listening to the described DigiOne Streamer using a lower cost switched power supply and compared it to a clean power supply input using a Li-Ion battery pack. The difference was audibly very clear in favor of the battery supply. So, yes I may not need the ultra low noise as stated in the Linear Power supply referenced earlier (which I think is a unit that appeal to the more outrageous "demands"). Just looking for a solution that filters out clearly audible noise and which I can put together for substantially lower cost (and I do not wish to use a li-Ion pack as that requires constant attention to charge).
 

Papabravo

Joined Feb 24, 2006
15,471
Sorry, but gone are the days where a handful of discrete components on a breadboard or even a PCB can match the performance of an integrated component. It is really tough to out do the silicon makers.
 

Thread Starter

bjornkarl

Joined Mar 14, 2021
8
Sorry, but gone are the days where a handful of discrete components on a breadboard or even a PCB can match the performance of an integrated component. It is really tough to out do the silicon makers.
I believe you are right! I will pursue a solution with a battery powerpack instead. A 20000mAh pack should give me about a day of use before needing a charge.
 

Thread Starter

bjornkarl

Joined Mar 14, 2021
8
Why are you reversing gears and going with a battery, when a low-noise linear IC regulator would likely be more than adequate?
I'm not reversing gears entirely. I will put together a linear regulator and test side by side with a battery to see if I can hear the difference.
 
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